Existing integrated circuit (IC) manufacturing lines typically include large clean rooms and some manufacturing tools in the clean rooms, while other tools, such as the tools that are used for metrologies and/or wafer transferring/transporting/exchanging paths, are within relatively open environments. When exposed to the open environment, wafers are vulnerable to the attacks of adverse substances such as moisture, oxygen, and various airborne molecular contaminants (AMC) sources, which include etching byproduct solvents, perfumes, storage materials, chamber residual gases, etc. An example of the AMCs is dimethyl sulfide (DMS), which is a chemical commonly used in the semiconductor manufacturing processes.
As the semiconductor processes precede into the nanometer domain, the negative effects of adverse substances on IC manufacturing become increasingly more severe. For example, in some critical stages, AMCs have posted serious problems impacting either device performance or metrology accuracy. Furthermore, in the formation of copper features in metallization layers, due to the very small size of copper features, the reaction caused by oxygen, moisture, and the AMC sources causes an increase in RC delay of the manufactured integrated circuits, and sometimes a reduction in production yield. Low-k dielectric materials for forming metallization layers are also vulnerable to the attack of chemicals such as acids.
Existing IC manufacturing lines do not provide effective means for protecting wafers from the above-discussed problems. Therefore, methods have been explored to reduce the adverse substances. For example, efforts have been made to reduce the interval (Q time) between process stages. Cassettes or Front Opening Unified Pod (FOUP) were also periodically cleaned to remove possible adverse substances.